Regarding electronics, you can take one each of whatever you have listed without paying taxes. The Nepal Customs law states that traveller can bring in 1 each of some electronics goods (I don't remember the list, but the things you've listed fall under it) for personal use without paying any customs. But, to be on the safe side and avoid unneccesary arguments, make the things look like they are not brand new; you can take them without their cases or with opened cases. The other camera you're taking, just tell them that they are for your family members if they ask you; but normally, if you don't have big TV's or largely visible goods, they don't bother asking you unless you show them yourselves or provide them specific details.

I hope you are considering taking the electronics in your hand carry rather than in luggages.

Good Luck and happy journey!